Abstract This purpose of this K23 Mentored Patient-Oriented Career Development Award is to expedite the candidate's development into an independent investigator with expertise in the conduct of behavioral intervention studies to reduce alcohol use and alcohol-related consequences among young adults who present to the Emergency Department (ED) for care. Within this 5 year award, focused training will be dedicated to gain expertise in: 1) psychological theories of alcohol use and behavior change; 2) behavioral interventions to prevent hazardous alcohol use; 3) computerized approaches to deliver behavioral interventions; and 4) mixed methodology analyses. The candidate will perform three studies over the course of the award to apply these acquired skills and to optimize an interactive, computerized, text-messaging (SMS) delivered, behavioral intervention to prevent hazardous alcohol use among young adults. This intervention builds upon the candidate's experience developing and testing SMS-delivered behavioral interventions and incorporates strategies to increase young adult motivations to set drinking limits prior to planned drinking occasions, reinforce goal limits during drinking episodes and assist reflection the day after drinking episodes. Communication will take place Thursday through Sunday every week, will be tailored to baseline data, and adaptive to ecological momentary assessments (EMA) of alcohol cognitions and use patterns. In Study #1, the candidate will perform focus groups with 40 young adults with hazardous drinking to identify acceptability and preferences for an SMS intervention incorporating these features. In Study #2, the candidate will test the feasibility of a user-informed SMS intervention over a 12-week period with 40 young adults identified in the ED with hazardous drinking. Assessments will be completed at baseline, through EMA reports and at week 12 via a web-based follow-up. Primary outcomes include fidelity to EMA (including intra-drinking dialogue) over 12 weekends and end-of-study ratings of program usability. In Study #3, the candidate will conduct a 3-arm RCT with 90 young adults identified in the ED with hazardous drinking to compare estimates of efficacy of an SMS intervention incorporating pre-, intra-and post- drinking support dialogue to an SMS intervention incorporating pre-and post-drinking support dialogue (no intra-drinking support) and an SMS assessment control group. Primary outcomes include weekend heavy drinking episodes and average drinks per drinking episode as measured through EMA reports. Additional outcomes will include total drinks per month, alcohol-related consequences, and intervention satisfaction as measured through web-based follow-up assessments. Outcomes will be used to modify the intervention and to prepare for a larger Phase III RCT. The focus of this project fits with the NIAAA's Lifespan perspective on alcohol use. The training proposal and research plan fits with the NIAAA initiatives to reduce college and underage drinking. The ED population we plan to study fits with the NIAAA strategic objectives to focus on reducing health disparities among minority groups and non- student populations.